Emission after-treatment devices may be used to treat exhaust gas of internal combustion engines. In particular, emission treatment devices may include particulate filters, oxidation catalysts, and nitrogen oxide (NOx) catalysts. Particulate matter, which is largely made up of carbon particles from incomplete combustion, may be collected in particulate filters and may gradually restrict a flow of an exhaust gas as the particulate matter accumulates in the particulate filters. In order to periodically regenerate or purge the filter of particulate matter, measures may be taken that result in an increase of the exhaust gas temperature above a predetermined level (e.g. above 450° C.) in order to incinerate the carbon particles accumulated in the filter.
In some cases, a particulate filter reaches high enough exhaust temperatures during normal vehicle operation to passively perform a particulate filter regeneration. However, some vehicles may not reach passive regeneration conditions (e.g., vehicle speeds above 40 mph) and the particulate filter may become fouled. A regeneration of the particulate filter may additionally or alternatively occur during deceleration fuel shut off operating conditions (DFSO). DFSO is a mode to increase fuel economy and reduce brake wear in motor vehicles with a powertrain that normally operates at stoichiometry. In this approach, fuel injection to one or more cylinders is disabled during select operating conditions.
In some cases, a vehicle may perform a particulate filter regeneration during DFSO based on an estimated soot load and particulate matter reaction rate. An estimated soot load may be based on an exhaust backpressure measured upstream of the particulate filter. A particulate matter reaction rate may be calculated based on the estimated soot load. However, the inventors have found issues with the above identified operation. For instance, a soot load on a particulate filter may be difficult to estimate due to an accumulating ash load. The ash load may artificially increase the estimated soot load by increasing the exhaust backpressure, where the increase is mistaken for an increase in soot, resulting in an increased estimate of the particulate matter reaction rate and unnecessary reduction of the length of DFSO. Therefore, a DFSO particulate filter regeneration may be unnecessarily limited to protect the particulate filter against the combustion of a soot load that is not there. High particulate filter temperatures may cause particulate filter degradation which may include but is not limited to the particulate filter developing a leak or completely burning up (e.g., missing particulate filter).
However, the inventors have found various approaches to circumvent the issues listed above. In one example, the issues described above may be addressed by a method for adjusting a length of a deceleration fuel shut-off (DFSO) event and a total number of activated and deactivated cylinders during the DFSO based on a particulate filter temperature change during a particulate filter regeneration. Further, the length may be adjusted based on an assumed maximum soot load on the particulate filter. By assuming a maximum soot load on the particulate filter, a particulate matter reaction rate (e.g., rate at which soot is burned off the particulate filter) is dependent on oxygen availability. As one example, if a particulate matter reaction length is greater than the length of DFSO, then one or more cylinders of an engine may be activated during DFSO to reduce an oxygen flow and extend a length of DFSO to match the reaction rate of soot. In this way, the oxygen flow rate is decreased while still performing a particulate filter regeneration during DFSO. By doing this, the filter may not exceed a maximum allowed particulate filter temperature, therefore reducing the likelihood of a particulate filter degradation, while completing the particulate filter regeneration.
The above discussion includes recognitions made by the inventors and not admitted to be generally known. Thus, it should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.